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Be more careful when transforming | to +. Patch from Wojciech Matyjewicz.

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@44248 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Nick Lewycky 2007-11-20 08:24:44 +00:00
parent cec5f3003f
commit cf96db2c1d
2 changed files with 26 additions and 6 deletions
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14
lib/Analysis/ScalarEvolution.cpp
View File

@ -1484,25 +1484,27 @@ SCEVHandle ScalarEvolutionsImpl::createSCEV(Value *V) {
case Instruction::SDiv: case Instruction::SDiv:
return SE.getSDivExpr(getSCEV(I->getOperand(0)), return SE.getSDivExpr(getSCEV(I->getOperand(0)),
getSCEV(I->getOperand(1))); getSCEV(I->getOperand(1)));
break;
case Instruction::Sub: case Instruction::Sub:
return SE.getMinusSCEV(getSCEV(I->getOperand(0)), return SE.getMinusSCEV(getSCEV(I->getOperand(0)),
getSCEV(I->getOperand(1))); getSCEV(I->getOperand(1)));
case Instruction::Or: case Instruction::Or:
// If the RHS of the Or is a constant, we may have something like: // If the RHS of the Or is a constant, we may have something like:
// X*4+1 which got turned into X*4|1. Handle this as an add so loop // X*4+1 which got turned into X*4|1. Handle this as an Add so loop
// optimizations will transparently handle this case. // optimizations will transparently handle this case.
//
// In order for this transformation to be safe, the LHS must be of the
// form X*(2^n) and the Or constant must be less than 2^n.
if (ConstantInt *CI = dyn_cast<ConstantInt>(I->getOperand(1))) { if (ConstantInt *CI = dyn_cast<ConstantInt>(I->getOperand(1))) {
SCEVHandle LHS = getSCEV(I->getOperand(0)); SCEVHandle LHS = getSCEV(I->getOperand(0));
APInt CommonFact(GetConstantFactor(LHS)); APInt CommonFact(GetConstantFactor(LHS));
assert(!CommonFact.isMinValue() && assert(!CommonFact.isMinValue() &&
"Common factor should at least be 1!"); "Common factor should at least be 1!");
if (CommonFact.ugt(CI->getValue())) { const APInt &CIVal = CI->getValue();
// If the LHS is a multiple that is larger than the RHS, use +. if (CommonFact.countTrailingZeros() >=
(CIVal.getBitWidth() - CIVal.countLeadingZeros()))
return SE.getAddExpr(LHS, return SE.getAddExpr(LHS,
getSCEV(I->getOperand(1))); getSCEV(I->getOperand(1)));
}
} }
break; break;
case Instruction::Xor: case Instruction::Xor:

18
test/Analysis/ScalarEvolution/2007-11-18-OrInstruction.ll Normal file
View File

@ -0,0 +1,18 @@
; RUN: llvm-as < %s | opt -analyze -scalar-evolution 2>&1 | grep -e '--> %b'
; PR1810
define void @fun() {
entry:
br label %header
header:
%i = phi i32 [ 1, %entry ], [ %i.next, %body ]
%cond = icmp eq i32 %i, 10
br i1 %cond, label %exit, label %body
body:
%a = mul i32 %i, 5
%b = or i32 %a, 1
%i.next = add i32 %i, 1
br label %header
exit:
ret void
}